1. Field of the Invention
The present invention relates to a cylindrical vibration damping device in which a rubber bushing is retained in a condition of being press fit into a mounting member of cylindrical configuration, and more particularly relates to such a device in which an outer sleeve of the rubber bushing is formed of resin.
2. Description of the Related Art
Conventionally, cylindrical vibration damping devices have been widely used as trailing arm bushings, suspension bushings including torque rod bushings, engine mounts and the like for use in automotive vehicles. A typical cylindrical vibration-damping device has a design in which a rubber bushing, which includes rigid inner and outer sleeves elastically connected together via a rubber elastic body interposed therebetween, is held in press-fit fashion within a cylindrical bore of a mounting member, with an outer surface of the outer sleeve held in contact with an inner surface of the cylindrical mounting bore of the mounting member.
In a cylindrical vibration damping device of this kind, the outer sleeve, inner sleeve and mounting member of the rubber bushing are all made of metal. The outer sleeve of the rubber bushing is press fit into the cylindrical bore of the mounting member with a predetermined tightening allowance. This arrangement generates strong frictional force between the outer surface of the outer sleeve and the inner surface of the cylindrical bore of the mounting member, thus preventing undesirable dislodging of the rubber bushing from the mounting member.
Recently, fabricating the rubber bushing outer sleeve from resin has been considered. However, an inherent problem is that the elastic recovery force of a resin outer sleeve is depressed by means of stress relaxation, and when subjected to the effects of heat, even greater stress relaxation can be produced. Despite the predetermined tightening allowance during initial press fitting, changes over time result in depressed elastic recovery force of the outer sleeve vis-a-vis the mounting member, so that resistance to dislodging declines.
An exemplary countermeasure for this problem is disclosed in Reference 1 given hereinbelow. FIG. 28 shows a specific example, wherein 200 is a rubber bushing having a metal inner sleeve 202, a rubber elastic body 204 integrally disposed onto an outer surface of the inner sleeve 202, and a resin outer sleeve 206 integrally disposed onto an outer surface of the elastic body 204. 208 is a metal mounting member of cylindrical shape. The rubber bushing 200 is press fit into a bore of this mounting member 208 and retained fitting therein.
The resin outer sleeve 206 has a flange portion 210 at an axial end (the lower end as viewed in FIG. 28). This flange portion 210, by abutting the axial end face of the mounting member 208, prevents the rubber bushing 200 from dislodging in the upward direction in FIG. 28. The outer sleeve 206 has a partially thick-walled engaging portion 218, on the axial end thereof opposite from this flange portion 210 and projecting out in the axial direction from the mounting member 208. The partially thick-walled engaging portion 218 has sloping faces 214, 216 that incline in mutually opposite directions. Once the rubber bushing 200 has been press fit into the mounting member 208, the rubber bushing 200 is prevented from dislodging from the mounting member 208 in the downward direction in FIG. 28, by means of this engaging portion 218 becoming engaged with an axial end face of the mounting member 208, specifically, the axial end face on the opposite end from the flange portion 210.
[Reference 1]
JP-U-5-77637
However, the device taught in Reference 1, or shown in FIG. 11, has no specific provision for preventing rotation of the rubber bushing 200 relative to the mounting member 208, and if the resin outer sleeve 206 of the rubber bushing 200 that has been press fit into the mounting member 208 experiences depressed elastic recovery force due to stress relaxation, resulting in a likelihood of rotation of the rubber bushing 200 relative to the mounting member 208.
The cylindrical vibration damping device shown in FIG. 28 has the additional drawback that a portion of the outer sleeve 206, i.e., the area of the engaging portion 218, projects out in the axial direction from the mounting member 208 and lies exposed to the outside or the atmosphere. This makes it susceptible to deterioration. Another problem is that the portion lying exposed outside and projecting out from the mounting member 208 is susceptible to being struck by a flying pebble or the like and cracked.
A further problem with this cylindrical vibration damping device is that the axial length of the rubber bushing 200, specifically, the axial length of the portion excluding the flange portion 210, must be larger than that of the mounting member 208, and is therefore subject to limitations regarding shape.